One of the disturbing findings to emerge from studies on survivors of both childhood and adult cancers is the frequency with which systemic chemotherapy is associated with adverse neurological sequelae, including leukoencephalopathy, seizures, cerebral infarctions, and cognitive impairment. In our studies designed to understand the biological foundations for these effects, we have discovered that multiple mainstream chemotherapeutic agents applied at clinically relevant exposure levels are more toxic for the progenitor cells of the CNS and for non-dividing oligodendrocytes than they are for multiple cancer cell lines. Enhancement of cell death and suppression of cell division were seen in vitro and in vivo. When administered systemically in mice, these diverse chemotherapeutic agents caused increased cell death and decreased cell division in multiple regions of the CNS, with a high degree of correlation between in vitro observations and in vivo effects. Our current efforts are focused on three questions central to increasing our understanding of the biological underpinnings of the adverse neurological effects of cancer treatment and to developing means of preventing these effects. In this proposal, Aim 1 provides the first animal model of delayed CNS damage associated with chemotherapy and tests the hypotheses that (i) transient systemic administration of chemotherapy causes delayed damage to the CNS that is more severe than damage observed at short times after treatment;(ii) a particular target of damage is the myelinated white matter tracts of the brain;(iii) early indicators of delayed damage are dysregulation of transcription factor expression in myelin-forming oligodendrocytes, followed by marked reductions in oligodendrocyte numbers and an absence of oligodendrocyte replacement;and, (iv) delayed damage is also associated with reductions in the generation of new hippocampal neurons. Aim 2 provides the first paradigm for reducing or preventing such damage, and is focused on analysis of the hypothesis that co-treatment with erythropoietin (EPO) reduces CNS damage caused by chemotherapy. Aim 3 focuses on mechanism-based discovery of protective strategies for acute and delayed adverse effects of chemotherapy, and tests the hypotheses that (i) chemically diverse chemotherapeutic agents disrupt the function of primary cells -but not cancer cells - by convergence on a newly discovered regulatory pathway (the redox/Fyn/c-Cbl pathway) that converts small increases in oxidative state into enhanced degradation of a subset of receptor tyrosine kinases important in cell division and survival, with consequent reductions in activity of signaling molecules vital in cell division and survival;and, (ii) this prevention of activation of the redox/Fyn/c-Cbl pathway provides a mechanistic strategy for protecting primary cells from the adverse effects of chemotherapy without also rescuing cancer cells in bulk or cancer stem cells in particular. PUBLIC HEALTH RELEVANCE One of the disturbing findings to emerge from studies on survivors of both childhood and adult cancers is the frequency with which systemic chemotherapy is associated with adverse neurological sequelae, including leukoencephalopathy, seizures, cerebral infarctions, and cognitive impairment. The concern of our research is to understand the biological and mechanistic foundations for these adverse effects, both to discover means of protecting against such events and to develop means of identifying individuals at increased risk for adverse events. Such protection can be achieved both by increasing the vulnerability of cancer cells to chemotherapy and by selectively protecting normal cells from the adverse effects of these therapeutic agents.